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const countSubstrings = (str, searchValue) => {let count = 0,i = 0;while (true) {const r = str.indexOf(searchValue, i);if (r !== -1) [count, i] = [count + 1, r + 1];else return count;}};countSubstrings('tiktok tok tok tik tok tik', 'tik'); // 3countSubstrings('tutut tut tut', 'tut'); // 4
const geometricProgression = (end, start = 1, step = 2) =>Array.from({length: Math.floor(Math.log(end / start) / Math.log(step)) + 1,}).map((_, i) => start * step ** i);geometricProgression(256); // [1, 2, 4, 8, 16, 32, 64, 128, 256]geometricProgression(256, 3); // [3, 6, 12, 24, 48, 96, 192]geometricProgression(256, 1, 4); // [1, 4, 16, 64, 256]
const deepMerge = (a, b, fn) =>[...new Set([...Object.keys(a), ...Object.keys(b)])].reduce((acc, key) => ({ ...acc, [key]: fn(key, a[key], b[key]) }),{});deepMerge({ a: true, b: { c: [1, 2, 3] } },{ a: false, b: { d: [1, 2, 3] } },(key, a, b) => (key === 'a' ? a && b : Object.assign({}, a, b)));// { a: false, b: { c: [ 1, 2, 3 ], d: [ 1, 2, 3 ] } }
const getTimezone = () => Intl.DateTimeFormat().resolvedOptions().timeZone;// ExamplegetTimezone();
import React, { useState } from 'react' import Welcome from '../components/Welcome' function About() { const [showWelcome, setShowWelcome] = useState(false) return ( <div> {showWelcome ? <Welcome /> : null} </div> <div> {showWelcome && <Welcome /> } </div> ) } export default App
const nums = [1, 2, 3];const strs = Array.from('est');nums.push(6);nums.push(4, 9);strs.unshift('t');nums.length; // 6nums[nums.length - 1]; // 9strs[0]; // 't'strs[2]; // 's'nums.slice(1, 3); // [2, 3]nums.map(n => n * 2); // [2, 4, 6, 12, 8, 18]nums.filter(n => n % 2 === 0); // [2, 6, 4]nums.reduce((a, n) => a + n, 0); // 25strs.reverse(); // ['t', 's', 'e', 't']strs.join(''); // 'test'const nums = new Set([1, 2, 3]);nums.add(4);nums.add(1);nums.add(5);nums.add(4);nums.size; // 5nums.has(4); // truenums.delete(4);nums.has(4); // false[...nums]; // [1, 2, 3, 5]nums.clear();nums.size; // 0const items = new Map([[1, { name: 'John' }],[2, { name: 'Mary' }]]);items.set(4, { name: 'Alan' });items.set(2, { name: 'Jeff' });items.size; // 3items.has(4); // trueitems.get(2); // { name: 'Jeff' }items.delete(2);items.size; // 2[...items.keys()]; // [1, 4][...items.values()]; // [{ name: 'John' }, { name: 'Alan' }]items.clear();items.size; // 0